ENNS Catchment area. Upper Austria. Lower Austria. S t yria. Inn. Linz. Erlau. Ybb. Enns. Traun. Age. Enns

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1 TSCHECHIEN ENNS Catchment area Do na u Inn Upper Austria s Ybb Enns n Lower Austria Traun Ste yr Age r au Tr Erlau f Linz Enns S t yria 229

2 Measures in the Enns catchment area ERMANY Inn Donau Upper Austria Linz Salzach Ager Traun Enns Thurnsdorf Mühlrading Staning Pichlern Humpelmühle Enns Ybbs Erlauf Lower Austria Salzburg Steyr Traun Gstatterboden S alzburg Enns Styria N km River portrait of Enns catchment area The Enns is a southern tributary of the Danube and has the fifth-largest catchment area of all Austria rivers extending over 6,084 km². Being 254 km long, it is the longest river situated entirely within Austria and forms, in its lower course, the border between the federal provinces of Upper and Lower Austria. The Enns originates at an altitude of 1,735 m in the Lower Tauern group in Salzburg, flowing then northward through a transverse valley and at Reitdorf, the Enns turns eastward toward Styria. In Styria, after approx. 60 km, it changes its river course at a right angle near Hieflau and continues its flow northwards. The Enns reaches and passes through Upper Austria until, as a border river OESTERREICHS ENERGIE HYDROPOWER 230

3 between Upper and Lower Austria, it discharges to the Danube in Mauthausen. Along its course, the Enns overcomes 1,497 m. Over long stretches of its upper course, the Enns is a typical white-water river with a water flow that fluctuates heavily according to the season. In the middle course, near Admont, its water level amounts to an annual average of around 80 m³/s and reaches more than 200 m³/s at its confluence into the Danube. Fish fauna Due to its large extension, five different fish regions are classified along the Enns. Among the predominant fish species belonging to these fish regions are the barbel, the bream, the dace, the pike, the Danube salmon, the bleak, the nase and the ide. The target species on the Enns river is the Danube salmon with a length of 100 cm. Hence, all dimensions of the fish passage facilities are calculated according to the size and swimming performance of this species (see photo). Photo: VERBUND AG OESTERREICHS ENERGIE HYDROPOWER 231

4 Fish pass at the Gstatterboden dam at the Hieflau power plant Vertical slot passage of the fish pass Transition from the vertical slot passage into the near-natural bypass channel OESTERREICHS ENERGIE HYDROPOWER 232

5 Company Water body Water body number River kilometre VERBUND Hydro Power Enns GmbH Aim of measure Establishing ecological connectivity Type of measure Construction of a fish pass Description of measure At the Gstatterboden weir of the Hieflau power plant, the restoration of ecological connectivity was carried out through the construction of a fish pass in the second half of The approximately 270-metre-long fish pass on the orographic left side of the Enns bridges an altitude differential of around 10.9 m. It is composed of a vertical slot passage in the entrance area and a near-natural bypass channel that connects to it. The vertical slot pass consists of 48 ponds. The ponds were each designed with a length of 3.0 m, a width of 2.0 m, a minimum water depth of 75.2 cm, as well as a slot width of 30 cm, to accommodate the species referred to for dimensioning, the Danube salmon. The near-natural bypass channel was implemented over a length of around 225 m and has a slope of 2.0%. The channel width was implemented at 2.0 m, with a minimum water depth of 30 cm. The fish pass is provided with 322 l/s of water. Further, there is an additional attraction flow of 180 l/s in certain months. Period of construction/implementation (without monitoring) to Financial expenditures Total investment in 1,030,464.- Of which UFG funding 0.- (Estimated) monitoring expenditure in 48,543.- (Estimated) operating expenditure in /year 10,000.- Generation losses in MWh/year 281 MWh/year OESTERREICHS ENERGIE HYDROPOWER 233

6 Fish pass at the Humpelmühle power plant Fish pass on the downstream side Ponds of the fish pass OESTERREICHS ENERGIE HYDROPOWER 234

7 Company Water body Water body number River kilometre Energie AG OÖ Kraftwerke GmbH Steyr Aim of measure Establishing ecological connectivity Type of measure Construction of a fish pass Description of measure Taking into consideration the ecological constraints, at the Humpelmühle power plant an enature fish pass was integrated into the right bank on the downstream side, as near as possible to the turbine outlet. The connection to the downstream side, which is flush with the riverbed, is reached via a ramp with a constant substrate layer 20 cm thick. The transition to the head pond channel was implemented as a special console (sheet metal construction with gravel-filled gradations). In the area of the powerhouse, the transport channel of the Waste Water Treatment Association of Mittleres Steyrtal, which secures wastewater disposal for three municipalities, passes by. As a consequence of the restricted space, it is necessary that the fish pass pass under the powerhouse by means of an open channel pipeline with a continuous substrate layer 20 cm thick. In the area of the powerhouse entrance, the fish pass is covered with grating. The inlet structure in the head pond is furnished with a gate valve that is submerged at least 20 cm deep, in order to keep out floating debris. The outlet cross-section of the water body is not compromised by the fact that the fish pass is situated on the land side. When compared with a conventional vertical slot pond system with the same dimensions, the enature fish pass features around 20% lower flow velocities into the slots and a power density around 35% lower. Because of this, the 35 ponds are more easily passable especially for juveniles and for weak-swimming fish species. Period of construction/implementation (without monitoring) to Financial expenditures Total investment in 460,000.- Of which UFG funding 69,000.- Provincial state funding 50,000.- (Estimated) monitoring expenditure in 35,000.- (Estimated) operating expenditure in /year 7,500.- Generation losses in MWh/year 458 MWh/year OESTERREICHS ENERGIE HYDROPOWER 235

8 Fish pass at the Pichlern power plant Technical fish pass at the Pichlern power plant Near-natural channel of the fish pass at the Pichlern power plant OESTERREICHS ENERGIE HYDROPOWER 236

9 Company Water body Water body number River kilometre Ennskraftwerke AG Steyr Aim of measure Establishing ecological connectivity Type of measure Construction of a fish pass Description of measure In the course of the revitalisation and renovation of the Pichlern power plant facility between 2004 and 2006, a fish pass was constructed in order to restore the continuity of the Steyr. The structure is designed as a fish pass in a modular system. It is composed of a berm-like downstream ramp, a downstream entrance parallel to the turbine current, a vertical slot passage with a technical flat passage, a near-natural passage and an upstream residual water structure. This design ensures that, in addition to ecological connectivity, important habitat elements of river systems, such as spawning grounds or habitats for juveniles as well as valuable living space for benthic invertebrates, are also created. The overall length of the fish pass (technical section and natural passage) is about 290 m, whereby an altitude difference of around 5.6 m is bridged. The technical section is composed of a total of 41 ponds with a channel width of 1.5 m. With the exception of the three rest ponds, the individual ponds feature a length of 2.47 m. The water depth in the ponds is at least 70 cm, while the slot width is implemented at 25 cm. The energy density lies at around 117 W/m³. The natural passage is matched to the tributaries of the Steyr in its basic concept. The riverbed substrate is heterogeneous, between 0.2 cm and 6.3 cm thick. The banks feature no technical security measures. The incorporated rootstocks and stones secure the banks, form extremely heterogeneous structures and create cavities and fish shelters. Due to the redefinition of the parameters decisive for the dimensioning of fish passes which has taken place since the construction, the existing fish pass no longer conforms to the current requirements or to the Guidelines on the Construction of Fish passes published by the Austrian Federal Ministry of Agriculture, Forestry, Environment and Water Management in It must therefore be restructured in accordance with the renovation ordinance of the provincial governor of Upper Austria dated However, because it was able to be demonstrated in the context of the performance check that a substantial portion of the migratory individuals and stages of life of all main fish species are able to pass by, the renovation period in accordance with Section 2 Par. 2 of the renovation ordinance of the provincial governor of Upper Austria was extended from until Period of construction/implementation (without monitoring) 2004 to 2006 Financial expenditures Total investment in 340,000.- Of which UFG funding 0.- (Estimated) monitoring expenditure in 20,000.- (Estimated) operating expenditure in /year 5,000.- Generation losses in MWh/year 100 MWh/year OESTERREICHS ENERGIE HYDROPOWER 237

10 Fish pass at the Staning power plant Downstream connection of the existing fish pass Existing pond system ascent OESTERREICHS ENERGIE HYDROPOWER 238

11 Company Water body Water body number River kilometre Ennskraftwerke AG Enns Aim of measure Establishing ecological connectivity Type of measure Construction of a fish pass Description of measure The fish pass built at the Staning power plant in the course of the construction of the power plant at the end of the 1940s was optimised as far as was possible in the years between 1997 and 2000 starting from the original condition in accordance with the state of the technology at the time. The existing structure is conceived as a pond system with crown notches and holes, bridging an altitude difference of 14.2 m with 61 ponds. However, with regard to building type, dimensioning and residual water volume, the structure does not conform to the current state of the technology or to the Guidelines on the Construction of Fish passes published by the Austrian Federal Ministry of Agriculture, Forestry, Environment and Water Management in A renovation project was thus planned on the part of Ennskraftwerke AG which, due to the difficult local conditions, is conceived as a purely technical structure in the form of a slot pass. The project complies with the current guidelines with respect to its characteristics. Parallel with the application for the appropriate authorisation of the renovation project under water regulations, an extension of the deadline in accordance with Section 2 Par. 2 of the renovation ordinance of the provincial governor of Upper Austria dated was also requested. Period of construction/implementation (without monitoring) 1997 to 2000 Financial expenditures Total investment in 95,000.- Of which UFG funding 0.- (Estimated) monitoring expenditure in 15,000.- (Estimated) operating expenditure in /year 0.- Generation losses in MWh/year 197 MWh/Jahr OESTERREICHS ENERGIE HYDROPOWER 239

12 Fish pass at the Mühlrading power plant Ecological structure of the flat passage Structure of the lower natural passage Lower vertical slot section OESTERREICHS ENERGIE HYDROPOWER 240

13 Company Water body Water body number River kilometre Ennskraftwerke AG Enns Aim of measure Establishing ecological connectivity Type of measure Construction of a fish pass Description of measure The goal of the measure is to restore the continuity of the Enns at the Mühlrading power plant in accordance with the requirements of the WFD 2000, the national water management plan of 2009, and the renovation ordinance of the provincial governor of Upper Austria dated The structure is designed as a fish pass in a modular system. It is composed of a berm-like downstream ramp, a downstream entrance parallel to the turbine current, as well as alternating technical vertical slot passages and near-natural passages. A shallow water section is located in the middle of the fish pass. This design ensures that, in addition to ecological connectivity, important habitat elements of river systems, such as spawning grounds or habitats for juveniles as well as valuable living space for benthic invertebrates, are also created. The overall length of the fish pass is around 770 m, with a maximum altitude difference to be bridged of around 8.2 m. The three technical sections are pond-based ascending structures composed of a total of 53 ponds with slots extending over the entire height. With the exception of the rest ponds, the individual ponds feature a length of 3.28 m and a width of 2.46 m. The water depth in the ponds is at least 1.18 cm, while the slot width, at 46 cm, is designed for the fish species referred to for dimensioning, the Danube salmon, and the residual water volume is set at 750 l/s. The energy density, at around 68 W/m³, is very low. In order to compensate for possible reservoir water level fluctuations of up to 1.2 m, the exit structure has three openings that can be blocked off with covers, each releasing residual water into a different pond. In their basic concept, the natural passages are matched to a natural tributary of the Enns. The riverbed substrate is heterogeneous, between 0.2 cm and 6.3 cm thick. The banks feature no technical security measures. The incorporated rootstocks and stones secure the banks, form extremely heterogeneous structures and create cavities and fish shelters. Period of construction/implementation (without monitoring) to Financial expenditures Total investment in 1,680,000.- Of which UFG funding 186,658.- Provincial state funding 1,000.- (Estimated) monitoring expenditure in 111,000.- (Estimated) operating expenditure in /year 10,000.- Generation losses in MWh/year 450 MWh/year OESTERREICHS ENERGIE HYDROPOWER 241

14 Fish pass at the Thurnsdorf dam Aerial view of shell construction of the natural passage Aerial view of the vertical slot passage by the upstream inlet OESTERREICHS ENERGIE HYDROPOWER 242

15 Company Water body Water body number River kilometre Ennskraftwerke AG Enns Aim of measure Establishing ecological connectivity Type of measure Construction of a fish pass Description of measure The goal of this measure is to restore the continuity of the Enns at the Thurnsdorf dam in accordance with the requirements of the WFD 2000, the national water management plan of 2009, and the renovation ordinance of the provincial governor of Upper Austria dated The structure is designed in a modular system as a fish pass. It is composed of a berm-like downstream ramp, a downstream entrance parallel to the turbine current, a technical shallow-water passage, a near-natural passage and a technical vertical slot passage with an upstream residual water structure. This design ensures that, in addition to ecological connectivity, important habitat elements of river systems, such as spawning grounds or habitats for juveniles as well as valuable living space for benthic invertebrates, are also created. The overall length of the fish pass (technical sections and natural passage) is around 1,325 m, with a maximum altitude difference to be bridged of around 10.5 m. The technical sections include a shallow-water passage around 62 m long in the downstream area, a 71-metre-long adapted vertical slot passage in the culvert section under the upstream channel, as well as a vertical slot passage around 70 m long with an exit in the uppermost section of the fish pass. All system components are dimensioned such that the possibility of ascent is ensured both for weak-swimming fish species and juveniles, as well as for adult fish. Taking into consideration the fish species referred to for dimensioning, the Danube salmon, the ponds of the vertical slot pass are implemented with a length of 3.28 m and a width of 2.46 m. The water depth in the ponds is at least 1.18 cm, while the slot width is set at 35 cm. In the area of the culvert stretch, the vertical slot construction is adapted to the structural conditions. The partitions in this area are implemented as mobile elements for maintenance reasons. In order to compensate for the water level fluctuations of 100 cm on the upstream side, two inlets are planned. The deeper inlet, which is oriented toward the min. water level, is controlled via a water-level-dependent regulating cover. The approximately 1,110-metre-long natural passage is matched to the natural tributary of the Enns in its basic concept as well as in the riverbed substrate. The banks feature no technical security measures. The incorporated rootstocks and stones secure the banks, form extremely heterogeneous structures and create cavities and fish shelters. Period of construction/implementation (without monitoring) to Financial expenditures Total investment in 1,705,066.- Of which UFG funding 255,760.- Provincial state funding 50,000.- (Estimated) monitoring expenditure in 130,000.- (Estimated) operating expenditure in /year 10,000.- Generation losses in MWh/year Around 430 MWh/year OESTERREICHS ENERGIE HYDROPOWER 243

16 Residual water adaptation at the Thurnsdorf dam View from the dam onto the connecting residual water stretch OESTERREICHS ENERGIE HYDROPOWER 244

17 Company Water body Water body number River kilometre Ennskraftwerke AG Enns Aim of measure Increased residual water output Type of measure Installation of a residual water turbine Description of measure The goal of this measure is to improve the residual water regime in the diverted stretch below the dam in accordance with the requirements of the WFD 2000, the national water management plan of 2009, and the renovation ordinance of the provincial governor of Upper Austria dated The measure is intended to ensure year-round connectivity for as many potentially appearing aquatic organisms as possible in the diverted river stretch. The base level of residual water for the diverted river stretch is set at 19.5 m³/s based on a study commissioned on behalf of the Government of Upper Austria. The release of most of the base flow here takes place via a new residual water turbine with a flow rate of 19 m³/s. Although the development of energy efficiency in the residual water stretch (Thurnsdorf dam and Enns power plant) raises the production of these facilities, the heightened volume of released residual water into the residual water stretch leads to underproduction at the St. Pantaleon diversion hydropower plant. Period of construction/implementation (without monitoring) to Financial expenditures Total investment in 14,000,000.- Of which UFG funding 0.- (Estimated) operating expenditure in /year 0.- Generation losses in MWh/year 5,400 MWh/year OESTERREICHS ENERGIE HYDROPOWER 245

18 Fish pass at the Enns power plant Enns power plant with fish pass OESTERREICHS ENERGIE HYDROPOWER 246

19 Company Water body Water body number River kilometre Ennskraftwerke AG Enns Aim of measure Establishing ecological connectivity Type of measure Construction of a fish pass Description of measure The goal of the measure is to restore the continuity of the residual water stretch of the Enns at the Enns power plant (Enns auxiliary weir) in accordance with the requirements of the WFD 2000, the national water management plan of 2009, and the renovation ordinance of the provincial governor of Upper Austria dated This ensures year-round connectivity for as many potentially appearing aquatic organisms as possible. This structure is designed as a fish pass in a modular system. The fish pass is composed of a berm-like downstream ramp, a downstream entrance parallel to the turbine current, a technical vertical slot passage, a near-natural passage and an upstream residual water structure. This design ensures that, in addition to ecological connectivity, important habitat elements of river systems, such as spawning grounds or habitats for juveniles as well as valuable living space for benthic invertebrates, are also created. The overall length of the fish pass with the technical section and the natural passage is around 250 m; the maximum altitude difference to be bridged lies at 5.2 m. The technical section is composed of an ascent structure with a total of 38 ponds with vertical slots extending over the entire height. With the exception of the rest ponds, the individual ponds feature a length of 3.28 m and a width of 2.46 m. The water depth in the ponds is at least 1.18 cm. The slot width, at 35 cm, is designed for the fish species referred to for dimensioning, the Danube salmon. The energy density, at around 76 W/m³ in the normal ponds and less than 50 W/m³ in the rest ponds, is very low. In its basic concept, the natural passage is matched to a natural tributary of the Enns. The riverbed substrate is heterogeneous, between 0.2 cm and 6.3 cm thick. The banks feature no technical security measures. The incorporated rootstocks and stones secure the banks, form extremely heterogeneous structures and create cavities and fish shelters. Period of construction/implementation (without monitoring) to Financial expenditures Total investment in 965,100.- Of which UFG funding 103,404.- Provincial state funding 50,000.- (Estimated) monitoring expenditure in 156,000.- (Estimated) operating expenditure in /year 10,000.- Generation losses in MWh/year Around 210 MWh/year OESTERREICHS ENERGIE HYDROPOWER 247